Use of Java 8 Lambdas with Generics

Question

Is it possible to do this using Predicate interface.

I have a client class that utilizes functions provided by a MathUtility class. Whatever the Mathmatical operation it

Answer 1

Is there a way to do it without writing a sum function for every possible type of T that i'm expecting?

As Aaron Davis stated in a comment above, you can pass the reduction parameters to the method itself.

public static  T sumWithCondition(List numbers, Predicate condition, T identity, BinaryOperator accumulator) {
    return numbers.parallelStream().filter(condition).reduce(identity, accumulator);
}

An example would be:

List list = Arrays.asList(1, 2, 3, 4, 5);

System.out.println(sumWithCondition(list, i -> i > 1, 0, (a, b) -> a + b));

>> 14

List list2 = Arrays.asList(BigInteger.ONE, BigInteger.ONE);

System.out.println(sumWithCondition(list2, i -> true, BigInteger.ZERO, (a, b) -> a.add(b)));

>> 2